The thiosulfate ion, S2O32−, is a structural analogue of the SO42− ion in which one oxygen atom is replaced by one S atom. However, the two sulfur atoms in S2O3−2 are not equivalent. One of the S atoms is a sulfide-like sulfur atom that gives the thiosulfate its reducing properties and complex-forming abilities.

Thiosulfates are used in leather tanning, paper and textile manufacturing, flue-gas desulfurization, cement additives, dechlorination, ozone and hydrogen peroxide quenching, coating stabilizers, as an agricultural fertilizer, as a leaching agent in mining, and so on.
Due to these complex-forming abilities with metals, thiosulfate compounds have also been used in commercial applications such as photography, waste treatment and water treatment applications.
Thiosulfates readily oxidize to dithionates, trithionates, tetrathionates, and finally to sulfates:2S2O32−+3O2→2S2O62−S2O62−+O2→2SO42−7S2O32−+3/2O2→2S3O62−+2S4O62−2S3O62−+6O2→6SO42−S4O62−+5O2→4SO42−
Due to this transformation, thiosulfates are used as fertilizers in combination with cations such as ammonium, potassium, magnesium and calcium. The ammonium, alkali metal and alkaline earth thiosulfates are soluble in water. Water solubility of thiosulfates decrease from ammonium to alkali metals to alkaline earth thiosulfates.
Potassium (K) is a primary plant nutrient. Potassium is associated with movement of water, nutrients, and carbohydrates in plant tissue. If potassium is deficient or not supplied in adequate amounts, growth is stunted and yields are reduced. Potassium stimulates early growth, increases protein production, improves the efficiency of water use, is vital for stand persistence in cold weather, and improves resistance to disease and insects.
Potassium thiosulfate fertilizer contains the highest percentage of potassium in liquid form, compared to other sources of potassium such as potassium chloride (KCl), potassium nitrate (KNO3), and potassium sulfate (K2SO4). In addition, it combines potassium with sulfur (17%) which is also an essential plant nutrient.
It is contemplated that potassium thiosulfate could be produced by several alternative routes such as:
I. Reaction of S and SO32− in neutral or alkaline medium
II. Reaction of S2− and SO3−2 (via SO2 and HSO32−)
III. Oxidation of Potassium Hydrosulfide (KSH)
IV. Ion Exchange reaction between alkaline thiosulfates and potassium chloride or nitrate
V. Salt exchange between alkaline thiosulfates and Potassium Chloride or Nitrate
VI. Oxidation of Potassium Polysulfide
However, some of these alternatives present serious difficulties or disadvantages. Route I and II are relatively long processes and require the use of sulfur dioxide SO2. Both these routes are described when the scrubbing of the air pollutant sulfur dioxide is an objective. Route III requires handling of potassium hydrosulfide as a raw material which is not favorable due to a hydrogen sulfide environment. Routes IV and V suffer from the drawback that ion exchange and salt exchange require expensive raw materials and equipment, and also require a step of final stripping due to the need for working with dilute solutions. Finally, the prior art has been unsuccessful in producing high purity potassium thiosulfate with a low amount of byproducts via Route VI as thiosulfates, in general, are susceptible to further conversion to sulfite and sulfate. Potassium thiosulfate products with relatively high level of impurities are not well suitable as liquid plant nutrient or liquid fertilizer because of insufficient storage stability and the presence of particulate matter.